The present disclosure relates to semiconductor devices made of group III nitride semiconductor exhibiting normally off characteristics and methods of manufacturing the devices, and more particularly to group III nitride semiconductor devices increasing operating currents and reducing on-resistance and methods of manufacturing the devices.
Application of group III nitride semiconductor to switching devices, high-output devices, and high-frequency devices are actively researched and developed due to its physical characteristics of a wide band gap, high breakdown field strength, and saturated electron drift velocity.
In particular, the following methods using a heterojunction field effect transistor (hereinafter referred to as “HFET” or simply referred to as “FET”) utilizing two-dimensional electron gas (hereinafter referred to as “2DEG”) generated at the interface between an AlxGa1-xN layer, where 0<x≦1, and a GaN layer, which are sequentially epitaxially grown on a semiconductor substrate, have been reported. Controlling a threshold voltage using a gate recess structure (see, for example, T. Oka et al., AlGaN/GaN Recessed MIS-Gate HFET with High-Threshold-Voltage Normally-Off Operation for Power Electronics Applications, IEEE ELECTRON DEVICE LETTERS, VOL. 29, NO. 7, pp. 668-670, 2008). Using a p-type gate control layer (see, for example, Japanese Patent Publication No. 2006-339561 and Japanese Patent Publication No. 2007-019309). Providing normally off operation by forming an AlGaN layer being a normally off barrier layer with a reduced thickness, etc.